This invention relates generally to imaging systems, and more particularly to methods and apparatus for medical imaging with improved resolution.
Diagnostic nuclear imaging is used to study radionuclide distribution in a subject, such as a patient. Typically, one or more radiopharmaceuticals or radioisotopes are injected into the subject. Gamma camera detector heads, typically including a collimator, are placed adjacent to a surface of the subject to monitor and record emitted radiation. At least some known gamma camera detector heads are rotated around the subject to monitor the emitted radiation from a plurality of directions. The monitored radiation data from the plurality of directions is reconstructed into a three dimensional image representation of the radiopharmaceutical distribution within the subject.
Generally, the resolution of a gamma camera degrades with increasing distance between the imaged organ and the detector. Therefore, it is desirable to place the gamma camera as close as possible to the patient to facilitate minimizing the loss of resolution. At least some known imaging systems use non-circular orbits, such as oval or elliptical orbits to facilitate maintaining the detectors positioned close to the patient during a scan. When the imaging system is configured for example, with a pair of gamma cameras in an “L” mode as is done when imaging the heart, and other organs, the gamma cameras are configured so they essentially touch one another along adjacent edges. Typical gamma cameras comprise a large scintillation crystal of NaI optically coupled to an array of Photo-Multiplying Tube (PMT). Signals from the array of PMTs are processed to yield the location of the scintillation event on the crystal in what is known as “Anger” camera, for example as disclosed in U.S. Pat. No. 3,011,057. Because of this construction, the gamma camera is less responsive near an outer periphery of the detector. The gamma camera detector is sized larger than the viewing area, and a volume of missing data is created proximate a surface of each detector where the volume is “seen” from only one of the detectors. Generally, the body of the patient is maintained spaced away from the surface of the detectors to avoid “missing data” that causes artifacts in the reconstructed image.